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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 8815
Experience:  23 Years Caterpillar Engine experience.
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i have a 99 3406e in a 96 w900l, truck suffered a power loss

Customer Question

i have a 99 3406e in a 96 w900l, truck suffered a power loss over several months,not very noticeable until hooked up to 45k after hauling pretty said two week injectors we replaced ,that fixed nothing, i finally replaced atmos.pressure sensor.that helped the stuttering ,air to air,turbo,are ok, put a different ecm out of another truck on it took off pretty strong, but now is back to missinng again, like pulling a plug wire off a 350 chevy and then putting it back on, or slamming choke closed then reopening it on an old gas chevrolet .It may run great for a while then bad missing for a while. less than 500 k on engine,any thoughts other than injectors wich is first words out of everyone in a 110 dollar an hour shop its been too?I know virtually everything thats been done to this truck so if u need more info just ask.
Submitted: 6 years ago.
Category: Heavy Equipment
Expert:  Cat Man replied 6 years ago.

Hi. Thanks for using JA! Sorry for the delay.


It sounds like you have done alot of good work so far. I know that situations like this can be very aggravating.



Since the air system from the turbo to the air to air core is good and I assume that your engine has good fuel pressure (65 tp 90 psi). There are 3 things that come to mind about your problem.


The first is the accuracy of the temperature and pressure sensors. I know that you have already replaced the atmospheric sensor, but whenever I have problem like this, I like to verify that the Boost, Intake Air temperature, fuel temperature, and atmospheric sensors are reporting accuractly when the problem is occuring on the engine. In order to do this, someone will need to have ET hooked to your engine while the porblem is occurring. I have seen sensors read way off causing the engine to have problems.


The next thing is an injector harness. I know that you have had some of the injectors replaced and well as the ECM, but I have seen the injector wiring harnesses under the valve cover cause a miss under load with no fault code.


And lastly, is the fuel supply and return lines to the engine. If they are restricted, it could cause the engine to miss. Also, problems with these lines will not show up on a DYNO because these lines are bypassed. Unless the operator runs the truck with the lines hooked up normally and not to the computer.


When your truck was run on the Dyno, did the problem happen?

Customer: replied 6 years ago.
Truck was consistantly lacking power when it was dynoed, all cat could say was burnt fuel percentages were low and horsepower under 300 you need 3500 dollars for injectors,was not happy with diagnosis.this was low power {all} the time, now after sensor and flow back valve or ball was replaced {the one in the fuel filter area},lift pump,etc. no power help . But wen i put on my cousins ecm she took off,but was short lived about 2 months, then this missing problem started,as you stated i believe there is a short in injector harness or there is something cooking a connection in the ecm ,i will pay u, but i wanted to chat a little more, i didnt know if accepting would end our chat.
Customer: replied 6 years ago.
Sorry i was going to mention that when pm is done the primary filter gives no problem when its changed. but when water sep fuel filter is changed engine will start and run terrible untill u pump primer a few times then runs guy says not normal but cant say why.also fuel pressure was checked going down the road and is actually a little higher than you specified,90 to 105. thanx
Expert:  Cat Man replied 6 years ago.

Thanks for the information.


Clicking the accept will not end our chat. We can talk as long as needed.


90 to 105 is too high for a 3406E. This high pressure can be caused by 2 things.


The relief valve in the transfer pump is stuck closed, or you have a return line restriction.


If the transfer pump is the cause of the high pressure, it will not cause low power. It may however cause a fuel leak at the secondary fuel filter or the hand priming pump.


If the return fuel line of the engine is restricted, it will elevate the system pressure up to the valve opening pressure of the transfer pump. Which happens to be 105 psi. A return line restriction will cause the fuel in the head to get hotter than it should, it turn will cause low power. When the fuel stays in the head too long, it will get hot and expand and possibly aerate. These will cause your problems with your engine.



Cat Man and 3 other Heavy Equipment Specialists are ready to help you
Customer: replied 6 years ago.
forgive my ignorance,but transfer pump in the front of the engine right?cat replaced that after saying low fuel percentages.any way both that and the return deal on the primer were truck has no set time to run this way,maybe 150 miles no prob, then suddenly like taking a plug off an injector then replacing it momentarily over and over and you can hear turbo trying to spool then not ,So running rough after changing the fuel water sep filter could b a prime loss,but where? thanks for your patience.
Expert:  Cat Man replied 6 years ago.

Thanks for the information.


Yes. The transfer pump is located on the front of the engine.


Does your truck have a fuel pressure gauge on it? IF not, I would recommend putting one in so that when this happens, you will see if there is a fuel pressure problem.


What about the line from the engine to the tank? Has it been checked?

Customer: replied 6 years ago.
the shop i use locally ran a line from filter housing to tank to see if feed line was at fault,this did not help but as i said this is when engine had cont power fuel temp gauge on truck as of now.everything we did was prior to changing ecm.the return line has not been checked ,this is why im so puzzled becauseive talked to many techs both shop and backyard,it seems to me if something is plugged up it would have continual loss of power like a dirty fuel filter, the other day i started truck at 42 degrees ambient temp and it missed and ranlike crap for almost 30 miles then it was like you flipped a run good switch,so far you have been the most help,and i hate beating this to death but as you know the single owner operator is being squeezed very hard these days and i want to spend my cash were it will do the most good.
Expert:  Cat Man replied 6 years ago.

No problem I am glad to help.


If the problem changes like flipping a switch, it could very well be a problem with the injector harness. It may be worth trying.


Normally, if there is a return line restriction, it is fairly constant of a problem.

Customer: replied 6 years ago.
ok thanks youve been helpful.
Expert:  Cat Man replied 6 years ago.

You are very welcome.


Thanks for the accept and bonus!